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Why does pasteurized milk still need refrigeration?

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Learn about food preservation and the various methods to preserve foodstuffs — food preservation An overview of food preservation.

Pasteurized milk requires refrigeration because the standard pasteurization process is not a sterilization method. While it effectively destroys pathogenic microorganisms and significantly reduces the number of spoilage-causing bacteria, it does not eliminate all microbes.12

Because the milk is not sterile and still contains small numbers of harmless bacteria, it remains a perishable product. If left at room temperature, these remaining microbes can multiply, leading to spoilage. Consequently, immediate cooling to below 4.4 °C (40 °F) is necessary to inhibit bacterial growth and maintain the product's quality for its typical shelf life of about 14 days.12

In contrast, ultra-high-temperature (UHT) pasteurization can produce shelf-stable milk that does not require refrigeration until opened. This is achieved by using higher temperatures (138–150 °C) combined with specialized, sterile packaging that prevents outside contamination.12